Modifications of circadian and circannual rhythms with aging.

Whereas biological rhythms are now fairly well documented in young healthy adults, reports in elderly are relatively few for obvious reasons, including the difficulty of setting groups matched in age, sociological and professional background, medical history, and not in need of specific medication. Aging may modify one or several parameters characterizing biological rhythms. The modifications are different from one function to the next, and great care should be given not to mistake changes attributable to the aging process with those resulting from physical and physiological impairment caused by passed environmental aggressions and diseases. Nevertheless, the increasing number of subjects reaching the age of 65 or older, thanks to medical progress, makes necessary establishing time-qualified references values in the aged, as this kind of investigation should lead to an improvement of the conditions and quality of life of elderly subjects.